Based on Jules Verne's novel Captain Grant's Children, In Search of the Castaways is a roller-coaster of a Disney film, making up in excitement what it lacks in credibility or coherence. Hayley Mills and Keith Hamshere play the children of long-missing ship's captain Jack Gwillim. By chance, a note stuffed in a bottle comes to the attention of the kids and professor Maurice Chevalier; the note contains the fragment of a map, which suggests that Gwillim is somewhere in South America. Only after enduring a series of life-threatening adventures do Chevalier and the kids discover that they should have been in Australia all along! Once they're finally in the correct corner of the world, our protagonists are bedeviled by gunrunner George Sanders, the fellow who'd set the captain adrift. With the help of Wilfrid Brambell, a looney ex-crew member of the captain's (and the fellow who sent the bottled message), Chevalier, Mills and Hamshere are finally reunited with Gwillim--and as a bonus, Mills has found a boy friend, in the person of Michael Anderson. It's typical of the crazy-quilt approach taken by In Search of the Castaways that Maurice Chevalier decides to sing a cheery song in a moment of dire peril. Even so, the film was ideal Saturday-matinee fodder for the kiddie trade in 1963.
~ Hal Erickson, All Movie Guide